A timing chain is composed of a number of link plates flexibly connected to one another to form an endless chain. The chain is driven by a sprocket on an engine crankshaft and in driving relationship with a sprocket on an engine camshaft, or with a plurality of sprockets in the case of an engine having more than one camshaft. The chain is typically guided by being in sliding relationship with a pivoted tensioner lever a fixed chain guide, or a combination thereof.
Hitherto, link plates having sliding edge surfaces that travel in direct contact with guide members have been designed for reduced friction between their guide-engaging edges and the cooperating guide surfaces in order to reduce vibration and noise, to improve durability, to reduce wear and heat, and to reduce the size and weight of the chain.
One known link plate is formed so that its edge which slidably contacts the guide member is convex toward the guide member in order to reduce the sliding area and thereby reduce friction. In another known link plate, concave grooves for retaining lubricant oil are provided on the guide-engaging edge to improve lubricant retention. These known link plates are disclosed in United States patent application publication 2008/020882.
Although the known link plate having a convex edge has a reduced sliding area and can reduce sliding friction, its performance is dependent on various conditions such as the speed of travel of the chain, transmission torque, and the viscosity of the lubricating oil. Under some operating conditions, depletion of lubricating oil can occur, resulting in vibration and excessive heat. Accordingly, it has been difficult to fabricate reliable link plates because of interrelationship between their shapes and the conditions of their operation.
In the case of link plates having concave grooves for retaining lubricant oil on their guide-engaging edges, it has been difficult to obtain optimum reduction in sliding friction because of the problem of lubricant depletion that the grooved link plates share with the link plates having convex edges, and also because of the difficulty in achieving a stable and homogeneous supply of lubricant to the link plates in the widthwise and traveling directions.